Pulse transformer using stripline windings

ABSTRACT

A pulse transformer uses a stripline to form the windings. In order to achieve symmetry and minimize reflections, the stripline is twisted at predetermined points in the winding so that the position of the stripline conductors relative to the core is changed. In one embodiment the stripline is twisted 180* each time it passes through the center of the toroidal core.

United States Patent [72] Inventor Merle l'laldeman, Jr.

Downers Grove, Ill. [21] Appl. No. 849,984 [22] Filed Aug. 14, 1969 [45] Patented Oct. 5, 1971 [73] Assignee The United States of America as represented by the United States Atomic Energy Commission [54] PULSE TRANSFORMER USING STRIPLINE WINDINGS 6 Claims, 5 Drawing Figs. [52] US. Cl 336/188, 333/84 M, 336/220, 336/223, 336/229 [51] Int. Cl 11011 27/28 [50] Field of Search 333/84, 84 M; 336/225, 229, 221, 223, 220, 188; 174/117, 117.1, 117.11

[ 56] References Cited UNITED STATES PATENTS 1,133,750 3/1915 Shaw 336/188X 1,504,276 8/1924 Shackelton 336/188 X 2,659,845 1 H1953 Calvert 336/223 X 2,676,309 4/1954 Armstrong 174/1 17.1 3,004,229 10/1961 Steams 338/84 M 3,158,181 11/1964 Gore 174/117UX 3,260,972 7/1966 Posch 333/84 M 3,304,364 2/1967 Hetherington 174/1 17 X FOREIGN PATENTS 712,656 6/1965 Canada 174/1 17 Primary Examiner-Thomas .l. Kozma Anarney-Roland A. Anderson ABSTRACT: A pulse transformer uses a stripline to form the windings. In order to achieve symmetry and minimize reflections, the stripline is twisted at predetermined points in the winding so that the position of the stripline conductors relative to the core is changed. In one embodiment the stripline is twisted 180 each time it passes through the center of the toide! w msmmum SIS?! $611,233

' sum 1 nrz 59 ii" 38 W ZZ W 29 a 7 Fl; 4 Merle HJZZSZEZGr M w 237 flti'orfigy PULSE TRANSFORMERUSING STRIPLINE WINDINGS CONTRACTUAL ORIGIN OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION Pulse transformers which are used with pulses having very fast rise times, for example of the order of 0.1 nanosecond from 10 to 90 percent, are difficult to construct without large magnitude reflections. If wire of conventional construction is used in the transformer, the reflections are extremely large. If a transmission line, such as coaxial cable, is used the magnitude of the reflections is lower but still of an undesirable magnitude.

It is therefore an object of this invention to provide an improved pulse transformer.

Another object of this invention is to provide a pulse transformer using stripline transmission line in which the windings are symmetrical and reflections are reduced to a minimum.

SUMMARY or THE INVENTION In practicing this invention a pulse transformer is provided comprising a core with stripline transmission line used for the transformer windings. The stripline is wound around the core and twisted so that the conductors of the stripline are altemately positioned adjacent the core. The twisting is carried out so that the length of each conductor of the pair of conductors in the stripline positioned adjacent'the core is equal. This form of construction permits the use of a transmission line capable of transmitting energy at high frequencies and a pulse transformer in which the winding configuration is symmetrical.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by the drawings of which:

FIG. 1 is a schematic of a pulse transformer;

FIG. 2 is a cross-sectional view of a form of stripline useful in carrying out this invention;

FIG. 3 is a cross-sectional view of a transformer incorporating the features of this invention; and

FIG. 4 is an isometric view of a transformer incorporating the features of this invention.

FIG. 5 is a perspective view of a transfonner incorporating the features of this invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a schematic representation of a pulse inverting transformer incorporating the features of this invention. The transformer includes a pair of windings l and 11 wound on a core 12. The input signal is applied to terminals 13 and 14 and the output is taken from terminals 16 and 17.

Referring to FIG. 2, there is an example of a stripline which may be used for the windings l0 and 11. This stripline has a pair of flat conductors 20 and 21 separated by a dielectric 23. Dielectric strips 25 and 26 are positioned on the outside of conductors 20 and 21 so that conductor 20 is positioned between dielectric strips 23 and 25 and conductor 21 is positioned between dielectric strips 23 and 26. The assembly of conductive and dielectric strips is held together by means of insulating cover portions 28 and 29. Conductors 20 and 21 are free to slide with respect to dielectric strips 23, 25 and 26 so that the stripline structure is very flexible. This permits the use of stripline in the construction of very small pulse transformers.

In FIG. 3 there is shown another form of flexible stripline which is suitable for use in winding very small pulse transformers. Conductors 30 and 31 are separated by insulator 32 in the same manner as conductors 20 and 21 are separated by insulator 13. The insulating strips 25 and 26 of FIG. 2 are not used and covers 33 and 34 are positioned directly adjacent conductors 30 and 31. Covers 33 and 34 are free to move relative to the conductors 30 and 31 and are joined at 35 and 36 to form a sealed enclosure for the stripline.

In order to decrease the friction between the insulators and conductors, insulators 23, 25, 26, 32, 33 and 34 may be made from a material having a low coefficient of friction such as the polytetrafluoroethylene TEFLON. For example, transformers have been constructed using toroid cores of one-half to fiveeighths inch OD, one-fourth to three-eighths inch ID and a thickness of from one-eighth to one-fourth inch. The stripline used was approximately 0.025 inch thick and from 0.025 to 0.125 inch wide. This stripline could be bent to a radius of approximately one sixty-fourth of an inch without introducing discontinuities in the stripline. While a stripline of special construction has been shown for construction of the transfonner of this invention in small sizes, a conventional stripline can be used if the pulse transformer is sufficiently large.

In FIGS. 4 and 5 the manner in which the stripline is wound on the core is illustrated. Core 37 may be of a ferrite material. In FIG. 4, conductor 38 is positioned closer to core 37 than conductor 39. If the winding'were continued in this manner the winding would be unsymmetrical and undesirable reflections would be present. In order to achieve symmetry the stripline is rotated through at point 40 so that conductor 39 is closer to core 37 than conductor 38. This twisting is repeated as often as necessary so that the length of conductor 39 adjacent core 37 is substantially equal to the length of conductor 38 adjacent core 37. By this means the windings are made symmetrical and the reflections minimized.

In FIG. 5 the windings of a complete transformer are shown. The transformer is wound on a toroid 41 which may be of ferrite material. The stripline 42 includes the two conductors 46 and 47. As the stripline passes through the center of the core it is rotated 180 so that the positions of conductors 46 and 47 are reversed relative to the core. The 180 twist is shown at points 43, 44 and 45. Turns 48 and 49 are also twisted but the twist is not visible in FIG. 5.

While a 180 twist as the turn passes through the center of the core is shown in FIG. 5, it is not necessary that the twist occur at this point. The twist can occur at any point in a turn and does not have to occur once in each turn. Also the amount of twist can be greater or less that 180 as desired. The stripline should be twisted so that the length of one conductor adjacent the core is substantially equal to the length of the other conductor adjacent the core.

In a pulse transformer which was constructed using stripline twisted as described in this invention, it was found that the VSWR was substantially constant andless than 1.3 from approximately 10 to 10 Hz. A commercially available parallel wire pulse transformer of similar rating had a VSWR which was relatively flat at an average of approximately 1.6 from 10' to 4.10". At 5.10 there was a dip in the VSWR to a value of 1.1. The VSWR then rose to 3.2 at 7.10 and 7.9 at 9.10 indicating a large amount of reflected energy at the higher frequencies.

It will be understood that the invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pulse transformer, including in combination. a magnetic core, stripline conductive means. including first and second conductors formed of equal width bare electrical conductive strips mounted in a rectangular configuration, first insulator means slidably positioned between and in direct contact with said first and second conductors to hold the same in spaced-apart relationship, second insulator means disposed about said first and second conductors and said first insulator means in a restraining slidable engagement with said pair of conductive strips, said stripline conductive means being wound about said core and twisted so that said first and second conductors are alternately adjacent said core with the length of said first conductor adjacent said core being substantially equal to the length of said second conductor adjacent said core.

2. The pulse transformer of claim 1 wherein, said stripline conductive means is wound about said magnetic core with a 5. The pulse transformer of claim 1 wherein, said second insulator means is formed of a flexible cover surrounding said first and second conductors and said first insulator means.

6. The pulse transformer of claim 1 wherein, said second insulator means includes a pair of insulating strips each positioned adjacent and in direct contact with a separate one of said first and second conductors to position each of said first and second conductors between said first insulator means and one of said pair of insulating strips, said pair of insulating strips being in slidable engagement with said first and second conductors, said second insulator means further including cover means surrounding said first and second conductors, said firstinsulator means and said pair of insulating strips and holding the same in desired relationship. 

1. A pulse transformer, including in combination, a magnetic core, stripline conductive means including first and second conductors formed of equal width bare electrical conductive strips mounted in a rectangular configuration, first insulator means slidably positioned between and in direct contact with said first and second conductors to hold the same in spaced-apart relationship, second insulator means disposed about said first and second conductors and said first insulator means in a restraining slidable engagement with said pair of conductive strips, said stripline conductive means being wound about said core and twisted so that said first and second conductors are alternately adjacent said core with the length of said first conductor adjacent said core being substantially equal to the length of said second conductor adjacent said core.
 2. The pulse transformer of claim 1 wherein, said stripline conductive means is wound about said magnetic core with a plurality of turns, said stripline conductive means further being twisted 180* in each of said plurality of turns.
 3. The pulse transformer of claim 2 wherein, said conductive means is twisted at the same point in each of said plurality of turns.
 4. The pulse transformer of claim 1 wherein, said magnetic core is a toroidal ferrite core, said stripline conductive means being wound about said core with a plurality of turns, each of said turns having said stripline conductive means twisted 180* as said stripline conductive means passes through the center of said core.
 5. The pulse transformer of claim 1 wherein, said second insulator means is formed of a flexible cover surrounding said first and second conductors and said first insulator means.
 6. The pulse transformer of claim 1 wherein, said second insulator means includes a pair of insulating strips each positioned adjacent and in direct contact with a separate one of said first and second conductors to position each of said first and second conductors between said first insulator means and one of said pair of insulating strips, said pair of insulating strips being in slidable engagement with said first and second conductors, said second insulator means further including cover means surrounding said first and second conductors, said first-insulator means and said pair of insulating strips and holding the same in desired relationship. 